This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to Japanese Patent Application No. 2000-093878 filed in Japan on Mar. 30, 2000; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to plating equipment, and more specifically relates to a plating barrel for plating objects such as electronic devices, etc., by immersing a barrel containing the objects into a plating solution and by applying a current.
2. Description of the Related Art
A plating barrel is used for plating a metal layer onto objects such as electric components. FIG. 4 is a schematic view of an example of a plating barrel of the conventional type.
This plating equipment comprises a barrel 21 which includes a part constructed of a mesh screen, etc., for allowing a plating solution to pass through, and cathodes 22 are placed in the interior of the barrel 21. First, a quantity of objects (not shown) such as multilayer ceramic capacitors and conducting media (not shown) such as steel balls are placed in the barrel 21. Then the barrel 21 is immersed into a plating solution 24 contained in a plating bath 23. Then, a current is applied between an anode 25 which is placed into the plating solution 24 and the cathodes 22, which are placed inside the barrel 21, while the barrel 21 is rotated in the plating solution 24. Accordingly, the objects are brought into contact with the plating solution 24 and the cathodes 22 via the conductive media, and are plated.
In the above-described plating barrel of the conventional type, the objects and the conductive media tumble inside the barrel 21 due to the rotation of the barrel 21. However, since the end surfaces 21a of the barrel 21 are flat and are vertical, the objects tend to accumulate at the end surfaces 21a so that the objects are no longer in contact with the conductive media. Thus, there is a problem where the thickness of the plating layers on the objects has a large variation.
In addition, cathode-lead connections 26 for connecting to the cathodes 22 in the barrel 21 have generally horizontal portions, which allows the objects to piled up on top of the cathode-lead connections 26. This causes another problem where the objects on the cathode-lead connections 26 may not be plated at all, and plating defects may occur.
The present invention aims to solve the above-mentioned problems. Accordingly, an object of the present invention is to provide a plating barrel which prevents the objects from piling up or stopping in order to avoid the occurrence of plating defects, and which reliably forms a plated layer having uniform thickness on each of the objects.
To attain the above-described object, a plating barrel according to one aspect of the present invention comprises a barrel which is rotatable, has an approximately cylindrical shape, and contains objects inside it, at least one cathode-lead connection which penetrates through the end surface of the barrel along the rotational axis of the barrel and which is supported in a manner such that the cathode-lead connection is rotatable relative to the barrel, at least one cathode which is placed inside the barrel and which is connected to the end of the cathode-lead connection, and at least one either conical or pyramidal attachment which is attached to the cathode-lead connection, in a manner such that the central axis of the attachments are the same as the rotational axis of the barrel, the vertices of the attachments point to the center of the barrel, and peripheral portions of the bases of the attachments at the opposite ends relative to the vertices are in proximity to the inside end surfaces of the barrel, so that the objects do not pass through the gaps between the bases and the inside end surfaces of the barrel. Thus, the piling up or stopping of the objects is avoided or prevented, so that a layer having a uniform thickness is reliably formed on each of the objects and plating defects are prevented.
In order to avoid and prevent the objects from piling up, the conical or pyramidal attachments preferably have vertices having an angle q (see FIG. 1) which is larger than 90xc2x0, so as to be an obtuse angle.
In the present invention, there are no restrictions regarding the actual shape of the attachments. The attachments may be exactly conical or pyramidal; or, the shape of the attachments may be modified somewhat. For example, the vertices of the attachments may be rounded, or they may be flattened to form a trapezoidal cross-section cone.
A plating barrel according to another aspect of the present invention comprises a barrel which is rotatable, has an approximately cylindrical shape, and contains objects inside it, at least one cathode-lead connection which penetrates through the end surface of the barrel along the rotational axis of the barrel and which is supported in a manner such that the cathode-lead connection is rotatable relative to the barrel, at least one cathode which is placed inside the barrel and which is connected to the end of the cathode-lead connection, and at least one either conical or pyramidal attachment which is attached to the barrel in a manner such that the central axes of the attachments are the same as the rotational axis of the barrel, the vertices of the attachments point toward the center of the barrel, and peripheral portions of the bases of the attachments at the opposite ends relative to the vertices are in contact with or in proximity to the inside end surfaces of the barrel, so that the objects do not pass through the gaps between the bases and the inside end surfaces of the barrel. Thus, from piling up or stopping of the objects is avoided or prevented, so that a layer having a uniform thickness is reliably formed on each of the objects and plating defects are prevented.
Since the conical or pyramidal attachment is attached to the barrel, the attachment rotates along with the barrel, so that the piling up or stopping of the objects is more effectively avoided or prevented.
A major part of the cathode-lead connection is preferably placed in the lower section of the barrel, i.e., below the rotational axis of the barrel.
When the major part of the cathode-lead connection is placed at a lower section of the barrel relative to the rotational axis of the barrel, the objects which pile up in the lower section of the barrel effectively contact the cathodes, which enhances the effectiveness of the present invention.
The conical or pyramidal attachment preferably covers nearly all of the horizontal portion of the cathode-lead connection so as not to expose the generally horizontal portion inside the barrel.
Since the conical or pyramidal attachment covers the generally horizontal portion of the cathode-lead connection so as not to expose the esentially horizontal portion inside the barrel, the objects cannot pile up on the generally horizontal portions of the cathode-lead connections. Accordingly, plating defects in which the objects are not completely plated with uniform thickness layers are effectively prevented.